The present invention relates to the preservation of a solid food product, and more particularly to the prolongation of the shelf-life of such food product. Even more particularly, the present invention relates to the deactivation of microorganisms on a surface of the food product and the prevention of reinfection of the food product by such microorganisms.
Fresh fruits, vegetables, and other food products, for example, strawberries, accumulate microorganisms, which as used herein includes bacteria, viruses, and fungi, from the air, ground, water and other sources with which they come into contact. These microorganisms, through various known mechanisms, cause the perishable food products to spoil, thereby significantly limiting the shelf-life of the food products. (Shelf-life is the period of time during which the perishable food product can be stored refrigerated or unrefrigerated, and remain edible and free from noticeable or harmful degradation or contamination by microorganisms.) As a result, methods and apparatuses suitable for deactivating, i.e., killing or sterilizing, such microorganisms and thereby extending the shelf-life of perishable foods, such as strawberries, oranges, tomatoes, zucchini, apples, and other edible food products, are desirable.
The photobiological effects of light, including infrared light (780 nm to 2600 nm; i.e., 3.9.times.10.sup.14 Hz to 1.2.times.10.sup.14 Hz), visible light (380 to 780 nm; i.e., 7.9.times.10.sup.14 Hz to 3.9.times.10.sup.14 Hz), near ultraviolet light (300 to 380 nm; i.e., 1.0.times.10.sup.15 Hz to 7.9.times.10.sup.14 Hz) and far ultraviolet light (170 to 300 nm; i.e., 1.8.times.10.sup.15 Hz to 1.0.times.10.sup.15 Hz), have been studied, and efforts have been made to employ light to deactivate microorganisms on food products or containers for food products. See, e.g., U.S. Pat. No. 4,871,559, issued to Dunn et al. (the '559 patent), incorporated herein by reference. One significant problem, however, with apparatuses and methods that merely use light to deactivate microorganisms is the problem of reinfection. This problem arises because foods, particularly fruits and vegetables, are generally shipped in bulk containers and are therefore subjected to airborne microorganisms.
Significant effort has been directed to aseptic packaging technology for packaging of sterilized food products in sterile packaging materials in order to provide preserved foodstuffs that are not readily reinfected with microorganisms. However, such methods and apparatuses have various disadvantages such as requiring that the food products, e.g., fresh fruit, be packaged so as to prevent cross contamination.
One example of an aseptic packaging system in combination with a photobiological food treatment apparatus is shown in the '559 patent. Short pulses of incoherent, broad spectrum light are used to preserve food products against microbial degradative processes. As a result, the teachings of the '559 patent provide significant shelf-life and stability enhancements to the food product. Application of pulses of high intensity, incoherent polychromatic light provides efficient, effective, high throughput processing and results in many practical and economic advantages. Moreover, the short duration and the spectral range of each pulse permits spatial localization of various of the preservative effects of the light pulses to a thin surface layer such as the surface of the food product or packaging material.
Problematically, however, the apparatus of the '559 patent uses an individual package for each of the food products it processes, or for small groups of such food products. In the later case, the food products are susceptible to cross contamination. Such packaging is relatively costly for use with fruits and vegetables, which are typically shipped in non-airtight boxes without individual packaging; does not conform to industry conventions for shipment of fruits and vegetables; requires the use of complex packaging apparatuses; and results in unwanted packaging waste for the consumer of such fruits and vegetables. Thus, what is needed is a low cost, simplified apparatus and method for deactivating microorganisms and for extending their shelf-life that does not require the use of complex or expensive packaging, gas mixtures, etc., and that does not require modification of conventional shipping practices used in the fruit and vegetable industry.
Another attempt to prolong the shelf-life of perishable food products consists of the application of microbiocides and/or microbiostats to the surface of the perishable food products. As used herein, the terms microbiocide and microbiostat include substances for killing or preventing the growth/reproduction of microorganisms (as the term microorganisms is defined herein). One example of microbiocides are chemical fungicides. Generally, the microbiocide and/or microbiostat is combined with an emulsifying agent and is then applied to the surface of the food product. The emulsifying agent aids in the application and action of the microbiocide and/or microbiostat agent, which ensure that the microbiocide and/or microbiostat agent remains on the surface of the food product and deactivates microorganisms during shipping until the food product is consumed.
Problematically, such microbiocides and microbiostats have come under increased scrutiny by various governmental agencies, and in some cases have been shown to be potential human carcinogens. As a result, several microbiocides and microbiostats that were once commonly applied to the surface of food products in order to prolong the shelf-life of the food products have been or could be banned by governmental agencies from use with food products. Therefore, an approach to prolonging the shelf-life of perishable food products, that does not require the use of a microbiocide or a microbiostat, such as a chemical fungicide, is highly desirable.
The present invention advantageously addresses the above and other needs.